1. Field of the Invention
The present invention relates to an image forming apparatus and a method therefor as well as a program and a storage medium thereof, and specifically relates to an image forming apparatus and a method therefore, a program and a storage medium having a color density adjusting section for adjusting color density of an image.
2. Description of the Related Art
As for conventional copying machines, and color copying machines in particular, there are models which adjust various kinds of color density parameters so as to make colors fixed in predetermined timing in the case of making multiple copies of multiple originals.
The predetermined timing is often set at every time when copying of a predetermined number of sheets of pare (e.g. 2,000 sheets of A4 paper) has finished, or every time when a predetermined period of time (e.g. one hour) has passed, for example.
In the case of the color copying machines for instance, the various kinds of color density parameters include a high bias voltage applied to a photosensitive member (a photosensitive drum or a photosensitive belt), an amount of emission of a laser element for forming a latent image on the photosensitive member and an amount of toner supplied to the photosensitive member.
The color density parameters change in value due to environmental changes (temperature, humidity, and the like) for each of members during execution of a print job in the short run and due to characteristic fluctuation of each of the members derived from aged deterioration (a charging characteristic of the photosensitive member, the amount of emission of the laser element, and the like) in the long run. Therefore, unless the color density parameters are adequately adjusted, the colors primarily change during the execution of a print job.
In the case of an electrophotographic color image, the changes in the colors mean changes in density reproducibility of each color of yellow (Y) toner, magenta (M) toner, cyan (C) toner and black (K) toner for expressing full color.
For instance, if the amount of toner supplied to the photosensitive member increases, the color density becomes accordingly denser. If a charging voltage applied to the photosensitive member increases, the amount of toner electrostatically adhering to the photosensitive member increases and the color density becomes accordingly denser. Furthermore, if power of a laser beam radiated on the photosensitive member increases, the latent image formed on the photosensitive member becomes denser, thereby increasing the amount of toner adhered to make the color density denser accordingly.
The Y toner, the M toner, the C toner, and the M toner are different in characteristic from each other. For instance, in a case where the power of the laser beam is increased by 10%, the densities of the Y toner, the M toner, the C toner, and the K toner increase by 5%, 12%, 10% and 2%, respectively. Thus, a degree of the color density increasing varies generally according to the color. Further, it is widely known that, for example, the M toner includes several tens of percent of a Y component, and hence increase of the color density of M requires not only increase of the amount of the M toner, but also adjustment of the amount of the Y toner, otherwise the color cannot be changed as desired.
Thus, it is known that the adjustment of the color density requires fine adjustment of respective colors of Y, M, C and K, and further, it generally takes several minutes to adjust the respective color densities.
However, in a case where this adjustment is normally performed, that is, if the adjustment timing is set at every 2,000 sheets for instance, the adjustment of the color density is to be started during the execution of the copy job on appearance of a user who makes 10 copies for each of 50 originals after printing of 1,800 sheets has been finished following the adjustment. Consequently, there occurs a problem that a next user waiting for completion of printing in front of an image forming apparatus is kept waiting during that time.
There are also many users who do not care much about stability of the colors as long as red is reddish and blue is bluish in expression. Even for such users, the color density adjusting process during the execution of the copy job induces unpleasantness.
As for this problem, there is proposed a technology of starting the copy job after adjusting the color density according to predicted values when starting the next copy job based on elapsed time from completion of the copy job or the elapsed time and the environmental conditions (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2004-347666, for instance).
Furthermore, there is proposed a technique of measuring the number of copies is measured, adjusting the color density if it is predicted, when the copy job is finished, that a color density adjusting mode will be started during the execution of the next job, and then clearing the measured number of copies (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2004-142250, for instance).
However, in the technique typified by Japanese Laid-Open Patent Publication (Kokai) No. 2004-347666, the timing of adjusting the color density according to the predicted values is based on the elapsed time from completion of the previous job. To this end, in a case where a printout of the previous job is comprised of a text-based job of a low printing duty, a degree of fatigue of the photosensitive member and the laser element is low so that the timing of adjusting the color density may be retarded. In a case where the job to be started takes a long time, there may occur the timing of adjusting the color density once more during the execution of the job. In that case, it is necessary to cancel the color density adjustment or interrupt the job once and start a normal color density adjustment.
In the technique typified by Japanese Laid-Open Patent Publication (Kokai) No. 2004-142250, the timing of adjusting the color density is based on the number of copies from completion of the previous job. To this end, in a case where the printout of the job last time is a job of a low print duty such as a text-based job, the degree of fatigue of the photosensitive member and the laser element is low so that the timing of adjusting the color density may be retarded. In a case where the job is started immediately after the previous job, the user eventually needs to wait for the time required for the color density adjustment.
As described above, there are also many users who do not care much about stability of the colors as long as red is reddish and blue is bluish in expression. There are also the cases where such users do not need the frequent adjusting process itself.